It has recently become possible to provide patients with implantable cardiac stimulating devices that detect various cardiac arrhythmias and respond by applying therapies, such as a series of electrical pacing pulses or a cardioversion or defibrillation shock, to a patient's heart. The sophistication of the device to be implanted in a particular patient depends to a large degree on the type of cardiac arrhythmia that patient has. For instance, if a patient suffers from bradycardia, a standard fixed-rate or rate-responsive pacemaker may be sufficient. If, however, a patient suffers from episodes of tachycardia, which may in turn lead to fibrillation, a more complex device such as an implantable cardioverter and/or defibrillator may be warranted. Typically, cardiac stimulating devices such as these can respond to different detected arrhythmias with varying levels of therapy. For instance, if an episode of tachycardia is detected, the device can apply a series of antitachycardia pulses to the heart. If, however, tachycardia persists, even after applying antitachycardia pulses, an appropriate response might be to apply a cardioversion shock.
Because the level of therapy applied to the heart depends on the type of arrhythmia a patient experiences, it is important for a cardiac stimulating device to use appropriate detection criteria to classify and confirm a patient's arrhythmia. For example, tachycardias can be classified into zones, each having a different threshold heartbeat rate. When a threshold has been exceeded for a predetermined period, the cardiac stimulating device confirms tachycardia and responds by applying antitachycardia therapy to the patient. By setting the thresholds correctly, the optimum response of the cardiac stimulating device to such an arrhythmia can be ensured. Further, within each zone a series of applicable therapies may be applied in an effort to terminate an arrhythmia episode. The detection thresholds and the therapies to be applied to the patient's heart can be individually programmed into a cardiac stimulating device by a physician, who uses a "programmer" which is typically microprocessor-based.
The programmer provides a user-friendly interface, such as a touch screen, with which a user can set the desired values of various adjustable parameters for the cardiac stimulating device. After the selected values of these parameters are input into the programmer by the user, the programmer transmits this data to the cardiac stimulating device via a telemetry head.
Each patient has a different cardiac condition, so it is advantageous for the physician to adjust the programmable parameters to maximize the performance of the cardiac stimulating device for each individual. It may be beneficial if a physician adjusts the detection criteria to be more sensitive, so that arrhythmias are confirmed more quickly and the appropriate therapy is applied as soon as possible. Also, the response of the device following arrhythmia detection can be controlled. For example, the most aggressive therapies, such as the application of a cardioversion shock, may only be applied after less aggressive therapies have been unsuccessfully used, although such a shock should always be applied to the patient early enough to avoid subjecting the patient to unnecessary danger associated with persistence of the abnormal rhythm.
A physician traditionally optimizes the antitachycardia settings of a cardiac stimulating device by inducing tachycardia in an anesthetized or sedated patient. The behavior of the device, which is surgically implanted in the patient, to the induced tachycardia is then observed to determine if the detection criteria that were selected are effective at confirming tachycardia and if the therapy that is applied is effective in ending the tachycardia episode.
However, inducing tachycardia an excessive number of times could be stressful to the patient's heart, so the physician can only use this procedure a limited number of times. Further, if the patient has an arrhythmia episode that is recorded "in the field," it would be beneficial if the physician could test various detection criteria using that recorded cardiac signal, because a cardiac signal captured in the field may more accurately reflect the patient's typical arrhythmias than the cardiac signal produced when tachycardia is induced in a patient. If the programmer could generate the patient's cardiac signal, the physician could optimize the selection of detection criteria without having to repeatedly induce the tachycardia in the patient. With a sufficiently sophisticated programming system, a programmer could recommend appropriate detection criteria and levels of therapy to a physician based on a recording of a patient's intrinsic cardiac signal taken during an arrhythmia episode. Further, if the performance of the cardiac stimulating device could be simulated, optimization could be performed more quickly than if the cardiac stimulating device's response to the cardiac signal had to be telemetered from the device following a detected episode.